The present invention relates to a method for fabricating a capacitor of a semiconductor; and, more particularly, to a method for forming a ruthenium (Ru) storage node of a capacitor.
The process of fabricating a capacitor in a semiconductor device with a linewidth no more than 0.1 xcexcm adopts a metal-insulator-metal (MIM) structure. Here, many researches has been carried out on the method for forming a storage node, and ruthenium (Ru) is usually used as a material for a storage node.
When Ru is used for a storage node, there are such advantages that the capacity is increased and leakage current is reduced. In the formation of a storage node, a chemical vapor deposition (CVD) method is usually used. Therefore, a process window providing stable step coverage in a concave structure needs to be secured.
Referring to FIGS. 1A and 1B, which are cross-sectional views illustrating the conventional process for forming a Ru storage node of a semiconductor, a related-prior art is described herein.
First, as described in FIG. 1A, an oxide insulation layer 11 is formed on the substrate 10 that is already formed with various semiconductor constituents, and a plug 12 is formed thereon to penetrate the insulation layer 11 and contact the substrate 10. The plug 12 contacts the impurity diffusion area (not shown) of the substrate 10, which is source/drain, and includes a TiN barrier layer 12A.
Subsequently, the upper surface of the insulation layer 11 is made planar by performing a chemical mechanical polishing (CMP) process. Then, a second insulation layer 13 is formed to a height of a storage node, and a concave part is formed to expose the surface of the barrier layer 12A by etching the second insulation layer 13 selectively. Subsequently, a Ru layer 14xe2x80x2 is formed along the profile of the second insulation layer 13 to form a storage node.
Subsequently, the concave part formed in the second insulation layer 13 is filled with a photoresist PR, as shown in FIG. 1B.
Thereafter, a storage nodes 14 separated from neighboring storages node is formed by etching the Ru layer 14xe2x80x2 without a mask. Subsequently, the remaining photoresist is removed by performing dry stripping, as shown in FIG. 1C. That is, an etching process is applied to the Ru layer 14xe2x80x2 and the photoresist with O2/CF4/H2O/N2 or O2/N2, and then residual products and remaining photoresist are removed with solvent.
Subsequently, the substrate is thermally treated to recover the characteristics of the storage node 14 deteriorated during the above etching process, and then a short cleaning process is performed with buffered oxide etchant, prior to the formation of a dielectric layer for the purpose of removing the impurities.
Meanwhile, a series of process for forming a capacitor is completed by forming a dielectric layer and plate electrode on the storage node 14, which are not illustrated in the drawings.
The conventional method for forming a capacitor storage node, as described above, has many disadvantages, which will be described hereinafter with reference to FIG. 2.
In the conventional process described above, if dry stripping is performed with CF4 gas to remove the remaining photoresist after the etching process to form the storage node 14, the CF4 gas penetrates to the storage node made of Ru, and damages the TiN barrier layer under the storage node.
In addition, due to the porous characteristic of a Ru layer, the photoresist still remains on the porous surface of the storage node. The remaining photoresist is not removed even in the subsequent cleaning process using solvent.
In the meantime, good storage node profile can be obtained from optimized gases, but this has a problem in reproducibility.
Besides CF4, O2 gas also has these problems. As shown in FIG. 2, O2 in the stripping gas is detected in the Ru storage node, too. Accordingly, it is hard to obtain stable characteristics of a storage node with the prior art.
It is, therefore, an object of the present invention to provide a method for forming a stable ruthenium (Ru) storage node of a semiconductor device.
In accordance with an aspect of the present invention, there is provided a method for forming a Ru storage node of a semiconductor device, The method includes the steps of: a method for forming a ruthenium (Ru) storage node of a semiconductor device, comprising the steps of: etching an insulation layer on a substrate and forming openings; depositing a Ru layer along the profile of the insulation layer and the openings; filling a photoresist in the openings; performing an etching process until the insulation layer between neighboring openings is exposed and forming isolated Ru storage nodes with the Ru layer in the openings; and removing residual photoresist and polymers with a solution including H2SO4 and H2O2.
The method of the present invention takes an advantage of the superior stability of Ru in acid environment to other metals, and removes residual polymers and photoresist remaining on the Ru storage node by performing cleaning with H2O2 and H2SO4. At the same time, this method can protect the TiN barrier layer under the storage node from being damaged, and simplifies the process by incorporating the conventional three-step process into one step.